1. Field of the Invention
The present invention relates to spinal instruments, especially for essentially smooth connecting rods comprising a bone anchor member having an anchor part separated from a projecting screwthreaded head, associated with a nut, by a polygonal section intermediate body, enabling screwing in the case where the anchor part is a screw and forming an abutment in its upper part, and a receiving and locking assembly adapted to receive said rod.
It also relates to a receiving and locking assembly adapted in particular to connect a rod to an anchor member.
2. Prior Art
Patent FR-2 657 775 describes rod type spinal instruments adapted to reduce and to contain the spine, comprising a grub screw with a screwthreaded cylindrical head receiving a part engaged on a screwthreaded head enabling locking of a connecting rod between a bearing portion of said part and the conical portion of a locknut engaged on the screwthreaded head.
This system locks the rod relative to the screws, but the orientation of the rod relative to the screw, which is orthogonal to the screw, is the same for all of the screws and cannot be modified.
French patent 2 693 365 describes rod type spinal instruments allowing some degree of adjustment of the angle between the respective axes of the rod and of the screw in a particular plane (i.e. without this plane being able to pivot about the axis of the rod) and locking of the rod to the screw in this position.
This device comprises a grub screw with a screwthreaded head having an intermediate body, a receiving and locking assembly engaged on said screwthreaded head by means of an oblong orifice and provided with a housing to receive the rod laterally of the screw and abutting on the spherical shape upper surface of the intermediate body. The frustoconical lower face of the nut screwed onto the screwthreaded head comes into contact, in an area opposite the area of contact with the rod, with a corresponding frustoconical surface on said receiving and locking assembly.
It is nevertheless desirable to have a receiving and locking assembly enabling the angle of the rod relative to the screw to be increased and thereby to reduce further the curvature of the rods and consequently the tension in the arrangement linking the various grub screws, whilst significantly improving the locking and therefore the rigidity of the assembly.
Document U.S. Pat. No. 5,222,954 describes spinal instruments for connecting rods in which the receiving and locking part 26 is in the form of an orifice 28 enabling the engagement of a projecting screwthreaded head 16 and a second orifice 34 the axis of which is perpendicular to the axis of the orifice 28 and which is adapted to receive the connecting rod 40. Note that this device does not allow the connecting rod to be oriented in all directions, which is possible with the device of the present invention.
Likewise, documents EP-A-585 518 and U.S. Pat. No. 5,352,226 do not allow the connecting rod to be oriented in all directions.
Document U.S. Pat. No. 4,771,767 requires the use of a screwthreaded rod, which has the disadvantage that it cannot be modified to adapt it to the deformation or to the anatomy of the spine.
The aim of the present invention is therefore to propose spinal instruments featuring improved locking of the connecting rod whilst allowing the rod to be oriented in all directions within a certain angle relative to the neutral axis.